The development of Diffuse Optical Tomography (“DOT”) for obtaining three-dimensional images of spatially varying absorption and scattering properties of a highly scattered media probed by near infrared light has been rapidly advancing. The clinical application of the DOT techniques to imaging breast cancer and brain pathology has shown increased promise. This is the case along with the appearance of preliminary results indicating the feasibility of extracting physiologically relevant information from the images reconstructed from the diffuse optical measurements. Because the inverse imaging problem for the DOT is ill-conditioned and generally under-determined, the image quality may likely suffer from poor spatial resolution and a sensitivity to measurement noise. This image quality can be improved by optimizing the geometry and the number of measurements being performed. However, significant improvements using such techniques may likely be obtained only by including previously-obtained information into the image reconstruction.
The use of a hard structural constraint provided by Magnetic Resonance Imaging (“MRI”) and Ultrasound Imaging (“UI”) techniques to reconstruct the optical diffuse image is known. In these conventional approaches, three-dimensional spatial information for different structures within the highly scattered medium are identified by the MRI or UI techniques, and a previously obtained optical diffuse image is reconstructed based on the MRI/UI image to obtain a resultant image. Specifically, it can be assumed that the boundaries of the structures identified by the MRI/UI technique also serve as the boundaries for piece-wise continuous structures within the diffuse optical image. Given these hard structural constraints, the DOT problem is then reduced to characterizing the optical properties within the specified target structures. Nevertheless, because the correlation between an MRI/UI contrast and a DOT contrast has not been explored, the validity of the assumption in the hard constraint has remained unclear.